Studies of the chemical selectivity of hapten, reactivity, and skin sensitization potency. 1. Synthesis and studies on the reactivity toward model nucleophiles of the (13)C-labeled skin sensitizers hex-1-ene- and hexane-1,3-sultones.

The potent skin sensitizers hex-1-ene- and hexane-1,3-sultone have been synthesized isotopically labeled with (13)C at reactive sites. The reactivity of 2-[(13)C]- and 3-[(13)C]hex-1-ene-1,3-sultones and of 3-[(13)C]hexane-1,3-sultone toward a series of model nucleophiles for protein amino acid residues, i.e., butylamine, diethylamine, imidazole, propanethiol, and phenol, was followed by (13)C NMR spectroscopy. The reactivity in water of hex-1-ene-1,3-sultone toward model nucleophiles follows the hard and soft acid and base theory with the hard nucleophiles (primary and secondary amine and phenate) mainly reacting at position 3 by S(N) substitution, and the soft nucleophiles (thiolate and imidazole) mainly reacting at position 2 by a Michael addition reaction. Hexane-1,3-sultone reacts with model nucleophiles at position 3 by S(N) substitution. Both saturated and unsaturated sultones are sensitive to hydrolysis when reacted in water.

Studies of the chemical selectivity of hapten, reactivity, and skin sensitization potency. 2. nmr studies of the covalent binding of the (13)c-labeled skin sensitizers 2-[13C]- and 3-[13C]hex-1-ene- and 3-[13C]hexane-1,3-sultones to human serum albumin.

3-[(13)C]- and 2-[(13)C]hex-1-ene-1,3-sultones (1a and 1b, respectively) and 3-[(13)C]hex-1-ene-1,3-sultone 2a were incubated with human serum albumin in phosphate buffer at pH 8.1. In both cases, the main reaction was a hydrolysis via an S(N) reaction at position 3, but several adducts were also formed. Hex-1-ene-1,3-sultone, which is a strong skin sensitizer, appears also to be a strongly oxophilic molecule reacting mainly at position 3 through an S(N) reaction to give adducts on tyrosines. This sultone was also able to react with a single lysine residue, also via an initial S(N) reaction at position 3, followed by an intramolecular Michael addition at position 2 to form a mixture of aziridinium intermediates which were subsequently hydrolyzed to give an amino alcohol derivative as the final product. The same reaction carried out on acetylated human serum albumin seems to indicate that the target lysine could be Lys199, which is known to be easily acetylated. Hexane-1,3-sultone, which is a weak sensitizer, appears to be an even more oxophilic molecule, making adducts on tyrosines through an S(N) reaction at position 3. No reaction was observed on Lys199. The difference in skin sensitization potential seems therefore to be more related to the selective ability of modifying lysine residues than to the more general ability to modify tyrosine residues.

Synthesis of a water-soluble analog of 6-methyl-3-N-alkyl catechol labeled with carbon 13: NMR approach to the reactivity of poison ivy/oak sensitizers toward proteins.

A 13-C labeled water soluble derivative of alkylcatechol was synthesized and reacted with human serum albumin in phosphate buffer at pH 7.4 in air to allow a slow oxidation of the catechol into orthoquinone. The formation of several adducts was evidenced by a combination of 13C and 1H-13C correlation NMR. Although some adducts could result from a classical o-quinone formation - Michael type addition, our results suggest that a second pathway, involving a direct reaction of a carbon centered radical with proteins could be an important mechanism in the formation of modified proteins.